sum聚合条件问题？

[albert_skynet]

对多表的b字段求和，并按a分组。
实现显示sum(b)>20的记录，where应该怎么样写？

select a,sum(b) from(select a,b from a union all select a,b from b) a  group by a

[中国风]

select a,sum(b)  b from(select a,b from a union all select a,b from b) a group by a having sum(b) >20

[linguojin11]

[Quote=引用楼主 albert_skynet 的帖子:]
对多表的b字段求和，并按a分组。
实现显示sum(b)>20的记录，where应该怎么样写？

SQL codeselect a,sum(b) from(select a,b from a union all select a,b from b) a group by a
[/Quote]

codeselect a,sum(b) from(select a,b from a union all select a,b from b) a  group by a having sum(b)>20

[幸运的意外]

select a,sum(b) as b from (select a,b from 表a union select a,b from 表b) T group by a having sum(b)>20
在取得多个表中的a,b字段的查询中,可以用内连接或左连接的方式抽取出来,这样效率更高一些.由于楼主您没有给出多个表的结构,所以暂时用了自然连接来代替.